Processing of DNS queries

ABSTRACT

A system, method and computer-readable medium for request routing. A client request processing a resource identifier for requested content transmits a first DNS query to a content delivery network service provider. The content delivery network service provider transmits an alternative resource identifier in response to the client computing device DNS query. The client computing device then issues a second DNS query to the same content delivery network service provider. The content delivery network service provider can then either resolve the second DNS query with an IP address of a cache component or transmit another alternative resource identifier that will resolve to the content delivery network service provider. The process can repeat with the content delivery network service provider&#39;s network until a DNS server resolves a DNS query from the client computing device.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/059,997, now U.S. Pat. No. 8,156,243, entitled “REQUEST ROUTING” andfiled on Mar. 31, 2008, the disclosure of which is incorporated hereinby reference.

BACKGROUND

Generally described, computing devices and communication networks can beutilized to exchange information. In a common application, a computingdevice can request content from another computing device via thecommunication network. For example, a user at a personal computingdevice can utilize a software browser application to request a Web pagefrom a server computing device via the Internet. In such embodiments,the user computing device can be referred to as a client computingdevice and the server computing device can be referred to as a contentprovider.

Content providers are generally motivated to provide requested contentto client computing devices often with consideration of efficienttransmission of the requested content to the client computing deviceand/or consideration of a cost associated with the transmission of thecontent. For larger scale implementations, a content provider mayreceive content requests from a high volume of client computing deviceswhich can place a strain on the content provider's computing resources.Additionally, the content requested by the client computing devices mayhave a number of components, which can further place additional strainon the content provider's computing resources.

With reference to an illustrative example, a requested Web page, ororiginal content, may be associated with a number of additionalresources, such as images or videos, that are to be displayed with theWeb page. In one specific embodiment, the additional resources of theWeb page are identified by a number of embedded resource identifiers,such as uniform resource locators (“URLs”). In turn, software on theclient computing devices typically processes embedded resourceidentifiers to generate requests for the content. Often, the resourceidentifiers associated with the embedded resources reference a computingdevice associated with the content provider such that the clientcomputing device would transmit the request for the additional resourcesto the referenced content provider computing device. Accordingly, inorder to satisfy a content request, the content provider would provideclient computing devices data associated with the Web page as well asthe data associated with the embedded resources.

Some content providers attempt to facilitate the delivery of requestedcontent, such as Web pages and/or resources identified in Web pages,through the utilization of a content delivery network (“CDN”) serviceprovider. A CDN server provider typically maintains a number ofcomputing devices in a communication network that can maintain contentfrom various content providers. In turn, content providers can instruct,or otherwise suggest to, client computing devices to request some, orall, of the content provider's content from the CDN service provider'scomputing devices.

With reference to previous illustrative example, the content providercan leverage a CDN service provider with the modification orsubstitution of resource identifiers associated with the embeddedresources. Specifically, the resource identifiers can reference acomputing device associated with the CDN service provider such that theclient computing device would transmit the request for the additionalresources to the referenced CDN service provider computing device.Typically, the content provider facilitates the utilization of a CDNprovider by including CDN-provider specific resources identifiers inrequested content (e.g., Web pages). This approach generally correspondsto an “offline” process implemented by the content provider in advanceof receipt of a request for the original content from the clientcomputing devices. Accordingly, modifications to resource identifiers,such as to provide alternative resources identifiers for the same CDNservice provider, to provide additional information utilized by CDNservice providers in processing the request for content and/or toidentify alternative CDN service providers, can become inefficient asthey typically require implementation of the offline process the contentprovider.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same become betterunderstood by reference to the following detailed description, whentaken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a block diagram illustrative of content delivery environmentincluding a number of client computing devices, content provider, and acontent delivery network service provider;

FIG. 2 is a block diagram of the content delivery environment of FIG. 1illustrating the registration of a content provider with a contentdelivery service provider;

FIG. 3 is a block diagram of the content delivery environment of FIG. 1illustrating the generation and processing of a content request from aclient computing device to a content provider;

FIG. 4 is a block diagram of the content delivery environment of FIG. 1illustrating the generation and processing of a DNS query correspondingto an embedded resource from a client computing device to a contentdelivery network service provider;

FIG. 5 is a block diagram of the content delivery environment of FIG. 1illustrating the generation and processing of a DNS query correspondingto a first alternative resource identifier from a client computingdevice to a content delivery network service provider;

FIG. 6 is a block diagram of the content delivery environment of FIG. 1illustrating the generation and processing of a DNS query correspondingto a second alternative resource identifier from a client computingdevice to a content delivery network service provider;

FIG. 7 is a block diagram of the content delivery environment of FIG. 1illustrating the generation and processing of embedded resource requestsfrom a client computing device to a content delivery network serviceprovider; and

FIG. 8 is a flow diagram illustrative of a request routing routineimplemented by a content delivery network service provider utilization aseries of alternative resource identifiers.

DETAILED DESCRIPTION

Generally described, the present disclosure is directed to routing ofDNS query from a client computing device corresponding to contentrequests by a network resource, such as content delivery network (“CDN”)service providers. Specifically, aspects of the disclosure will bedescribed with regard to the routing of a client computing device DNSquery within a content delivery network service provider domainutilizing one or more alternative resource identifiers. Although variousaspects of the disclosure will be described with regard to illustrativeexamples and embodiments, one skilled in the art will appreciate thatthe disclosed embodiments and examples should not be construed aslimiting.

FIG. 1 is a block diagram illustrative of content delivery environment100 for the management and processing of content requests. Asillustrated in FIG. 1, the content delivery environment 100 includes anumber of client computing devices 102 (generally referred to asclients) for requesting content from a content provider and/or a CDNservice provider. In an illustrative embodiment, the client computingdevices 102 can corresponds to a wide variety of computing devicesincluding personal computing devices, laptop computing devices,hand-held computing devices, terminal computing devices, mobile devices,wireless devices, various electronic devices and appliances and thelike. In an illustrative embodiment, the client computing devices 102include necessary hardware and software components for establishingcommunications over a communication network 108, such as a wide areanetwork or local area network. For example, the client computing devices102 may be equipped with networking equipment and browser softwareapplications that facilitate communications via the Internet or anintranet.

Although not illustrated in FIG. 1, each client computing device 102utilizes some type of local DNS resolver component, such as a DNS Nameserver, that generates the DNS queries attributed to the clientcomputing device. In one embodiment, the local DNS resolver componentmay be provide by an enterprise network to which the client computingdevice 102 belongs. In another embodiment, the local DNS resolvercomponent may be provided by an Internet Service Provider (ISP) thatprovides the communication network connection to the client computingdevice 102.

The content delivery environment 100 can also include a content provider104 in communication with the one or more client computing devices 102via the communication network 108. The content provider 104 illustratedin FIG. 1 corresponds to a logical association of one or more computingdevices associated with a content provider. Specifically, the contentprovider 104 can include a web server component 110 corresponding to oneor more server computing devices for obtaining and processing requestsfor content (such as Web pages) from the client computing devices 102.The content provider 104 can further include an origin server component112 and associated storage component 114 corresponding to one or morecomputing devices for obtaining and processing requests for networkresources from the CDN service provider. One skilled in the relevant artwill appreciate that the content provider 104 can be associated withvarious additional computing resources, such additional computingdevices for administration of content and resources, DNS name servers,and the like. For example, although not illustrated in FIG. 1, thecontent provider 104 can be associated with one or more DNS name servercomponents that would be authoritative to resolve client computingdevice DNS queries corresponding to a domain of the content provider.

With continued reference to FIG. 1, the content delivery environment 100can further include a CDN service provider 106 in communication with theone or more client computing devices 102 and the content providers 104via the communication network 108. The CDN service provider 106illustrated in FIG. 1 corresponds to a logical association of one ormore computing devices associated with a CDN service provider.Specifically, the CDN service provider 106 can include a number of Pointof Presence (“POP”) locations 116, 122, 128 that correspond to nodes onthe communication network 108. Each POP 116, 122, 128 includes a DNScomponent 118, 124, 130 made up of a number of DNS server computingdevices for resolving DNS queries from the client computers 102. EachPOP 116, 122, 128 also includes a resource cache component 120, 126, 132made up of a number of cache server computing devices for storingresources from content providers and transmitting various requestedresources to various client computers. The DNS components 118, 124 and130 and the resource cache components 120, 126 132 may further includeadditional software and/or hardware components that facilitatecommunications including, but not limited, load balancing or loadsharing software/hardware components.

In an illustrative embodiment, the DNS component 118, 124, 130 andresource cache component 120, 126, 132 are considered to be logicallygrouped, regardless of whether the components, or portions of thecomponents, are physically separate. Additionally, although the POPs116, 122, 128 are illustrated in FIG. 1 as logically associated with theCDN Provider 106, the POPs will be geographically distributed throughoutthe communication network 108 in a manner to best serve variousdemographics of client computing devices 102. Additionally, one skilledin the relevant art will appreciate that the CDN service provider 106can be associated with various additional computing resources, suchadditional computing devices for administration of content andresources, and the like.

With reference now to FIGS. 2-7, the interaction between variouscomponents of the content delivery environment 100 of FIG. 1 will beillustrated. For purposes of the example, however, the illustration hasbeen simplified such that many of the components utilized to facilitatecommunications are not shown. One skilled in the relevant art willappreciate that such components can be utilized and that additionalinteractions would accordingly occur without departing from the spiritand scope of the present disclosure.

With reference to FIG. 2, an illustrative interaction for registrationof a content provider 104 with the CDN service provider 106 will bedescribed. As illustrated in FIG. 2, the CDN content registrationprocess begins with registration of the content provider 104 with theCDN service provider 106. In an illustrative embodiment, the contentprovider 104 utilizes a registration application program interface(“API”) to register with the CDN service provider 106 such that the CDNservice provider 106 can provide content on behalf of the contentprovider 104. The registration API includes the identification of theorigin server 112 of the content provider 104 that will providerequested resources to the CDN service provider 106.

One skilled in the relevant art will appreciate that upon identificationof appropriate origin servers 112, the content provider 104 can begin todirect requests for content from client computing devices 102 to the CDNservice provider 106. Specifically, in accordance with DNS routingprinciples, a client computing device request corresponding to aresource identifier would eventually be directed toward a POP 116, 122,128 associated with the CDN service provider 106. In the event that theresource cache component 120, 126, 132 of a selected POP does not have acopy of a resource requested by a client computing device 102, theresource cache component will request the resource from the originserver 112 previously registered by the content provider 104.

With continued reference to FIG. 2, upon receiving the registration API,the CDN service provider 106 obtains and processes the registrationinformation. In an illustrative embodiment, the CDN service provider 106can then generate additional information that will be used by the clientcomputing devices 102 as part of the content requests. The additionalinformation can include, without limitation, client identifiers, such asclient identification codes, content provider identifiers, such ascontent provider identification codes, executable code for processingresource identifiers, such as script-based instructions, and the like.One skilled in the relevant art will appreciate that various types ofadditional information may be generated by the CDN service provider 106and that the additional information may be embodied in any one of avariety of formats.

The CDN service provider 106 returns an identification of applicabledomains for the CDN service provider (unless it has been previouslyprovided), and any additional information to the content provider 104.In turn, the content provider 104 can then process the stored contentwith content provider specific information. In one example, asillustrated in FIG. 2, the content provider 104 translates resourceidentifiers originally directed toward a domain of the origin server 112to a domain corresponding to the CDN service provider. The translatedURLs are embedded into requested content in a manner such that DNSqueries for the translated URLs will resolve to a DNS servercorresponding to the CDN service provider 106 and not a DNS servercorresponding to the content provider 104. Although the translationprocess is illustrated in FIG. 2, in some embodiments, the translationprocess may be omitted in a manner described in greater detail below.

Generally, the identification of the resources originally directed tothe content provider 104 will be in the form of a resource identifierthat can be processed by the client computing device 102, such asthrough a browser software application. In an illustrative embodiment,the resource identifiers can be in the form of a uniform resourcelocator (“URL”). Because the resource identifiers are included in therequested content directed to the content provided, the resourceidentifiers can be referred to generally as the “content provider URL.”For purposes of an illustrative example, the content provider URL canidentify a domain of the content provider 104 (e.g.,contentprovider.com), a name of the resource to be requested (e.g.,“resource.xxx”) and a path where the resource will be found (e.g.,“path”). In this illustrative example, the content provider URL has theform of:

http://www.contentprovider.com/path/resource.xxx

During an illustrative translation process, the content provider URL ismodified such that requests for the resources associated with thetranslated URLs resolve to a POP associated with the CDN serviceprovider 106. In one embodiment, the translated URL identifies thedomain of the CDN service provider 106 (e.g., “cdnprovider.com”), thesame name of the resource to be requested (e.g., “resource.xxx”) and thesame path where the resource will be found (e.g., “path”). Additionally,the translated URL can include additional processing information (e.g.,“additional information”). The translated URL would have the form of:

http://additional_information.cdnprovider.com/path/resources.xxx

In another embodiment, the information associated with the CDN serviceprovider 106 is included the modified URL, such as through prepending orother techniques, such that the translated URL can maintain all of theinformation associated with the original URL. In this embodiment, thetranslated URL would have the form of:

http://additional_information.cdnprovider.com/www.contentprovider.com/path/resource.xxx

With reference now to FIG. 3, after completion of the registration andtranslation processes illustrated in FIG. 2, a client computing device102 subsequently generates a content request that is received andprocessed by the content provider 104, such as through the Web server110. In accordance with an illustrative embodiment, the request forcontent can be in accordance with common network protocols, such as thehypertext transfer protocol (“HTTP”). Upon receipt of the contentrequest, the content provider 104 identifies the appropriate responsivecontent. In an illustrative embodiment, the requested content cancorrespond to a Web page that is displayed on the client computingdevice 102 via the processing of information, such as hypertext markuplanguage (“HTML”), extensible markup language (“XML”), and the like. Therequested content can also include a number of embedded resourceidentifiers, described above, that corresponds to resource objects thatshould be obtained by the client computing device 102 as part of theprocessing of the requested content. The embedded resource identifierscan be generally referred to as original resource identifiers ororiginal URLs.

Upon receipt of the requested content, the client computing device 102,such as through a browser software application, begins processing any ofthe markup code included in the content and attempts to acquire theresources identified by the embedded resource identifiers. Accordingly,the first step in acquiring the content correspond to the issuance, bythe client computing device 102 (through its local DNS resolver), a DNSquery for the Original URL resource identifier that results in theidentification of a DNS server authoritative to the “.” and the “com”portions of the translated URL. After resolving the “.” and “com”portions of the embedded URL, the client computing device 102 thenissues a DNS query for the resource URL that results in theidentification of a DNS server authoritative to the “.cdnprovider”portion of the embedded URL. The issuance of DNS queries correspondingto the “.” and the “com” portions of a URL are well known and have notbeen illustrated.

With reference now to FIG. 4, in an illustrative embodiment, thesuccessful resolution of the “cdnprovider” portion of the original URLidentifies a network address, such as an IP address, of a DNS serverassociated with the CDN service provider 106. In one embodiment, the IPaddress is a specific network address unique to a DNS server componentof a POP. In another embodiment, the IP address can be shared by one ormore POPs. In this embodiment, a further DNS query to the shared IPaddress utilizes a one-to-many network routing schema, such as anycast,such a specific POP will receive the request as a function of networktopology. For example, in an anycast implementation, a DNS query issuedby a client computing device 102 to a shared IP address will arrive at aDNS server component logically having the shortest network topologydistance, often referred to as network hops, from the client computingdevice. The network topology distance does not necessarily correspond togeographic distance. However, in some embodiments, the network topologydistance can be inferred to be the shortest network distance between aclient computing device 102 and a POP.

With continued reference to FIG. 4, in either of the above identifiedembodiments (or any other embodiment), a specific DNS server in the DNScomponent 118 of a POP 116 receives the DNS query corresponding to theoriginal URL from the client computing device 102. Once one of the DNSservers in the DNS component 118 receives the request, the specific DNSserver attempts to resolve the request. In an illustrative embodiment, aspecific DNS server can resolve the DNS query by identifying an IPaddress of a cache server component that will process the request forthe requested resource. As described above, a selected resource cachecomponent can process the request by either providing the requestedresource if it is available or attempt to obtain the requested resourcefrom another source, such as a peer cache server computing device or theorigin server 112 of the content provider 104.

As an alternative to selecting a cache server component, the CDN serviceprovider 106 can maintain sets of various alternative resourceidentifiers. The alternative resource identifiers can be provided by theCDN service provider 106 to the client computing device 102 such that asubsequent DNS query on the alternative resource identifier will resolveto a different DNS server component within the CDN service provider'snetwork. In an illustrative embodiment, the alternative resourceidentifiers are in the form of one or more canonical name (“CNAME”)records. In one embodiment, each CNAME record identifies a domain of theCDN service provider 106 (e.g., “cdnprovider.com” or“cdnprovider-1.com”). As will be explained in greater detail below, thedomain in the CNAME does not need to be the same domain found inoriginal URL or in a previous CNAME record. Additionally, each CNAMErecord includes additional information, such as request routinginformation, (e.g., “request routing information”). An illustrativeCNAME record can have the form of:

http://request_routing_information.cdnprovider.com

In an illustrative embodiment, the CNAME records are generated andprovided by the DNS servers to direct a more appropriate DNS server ofthe CDN service provider 106. As used in accordance with the presentdisclosure, appropriateness can be defined in any manner by the CDNservice provider 106 for a variety of purposes. In one example, the CDNservice provider 106 can attempt to direct a DNS query to DNS serversaccording to geographic criteria. The geographic criteria can correspondto geographic-based regional service plans contracted between the CDNservice-provider 106 and the content provider 104 in which various CDNservice provider 106 POPs are grouped into geographic regions.Accordingly, a client computing device 102 DNS query received in aregion not corresponding to the content provider's regional plan may bebetter processed by a DNS server in region corresponding to the contentprovider's regional plan. In this example, the DNS server component 118may also obtain geographic information from the client directly (such asinformation provided by the client computing device or ISP) orindirectly (such as inferred through a client computing device's IPaddress).

In another example, the CDN service provider 106 can attempt to direct aDNS query to DNS servers according to service level criteria. Theservice level criteria can correspond to service or performance metricscontracted between the CDN service provider 106 and the content provider104. Examples of performance metrics can include latencies of datatransmission between the CDN service provider POPs and the clientcomputing devices 102, total data provided on behalf of the contentprovider 104 by the CDN service provider POPs, error rates for datatransmissions, and the like.

In still a further example, the CDN service provider 106 can attempt todirect a DNS query to DNS servers according to network performancecriteria. The network performance criteria can correspond tomeasurements of network performance for transmitting data from the CDNservice provider POPs to the client computing device 102. Examples ofnetwork performance metrics can include network data transfer latencies(measured by the client computing device or the CDN service provider106), network data error rates, and the like.

In accordance with an illustrative embodiment, the DNS server maintainsa data store that defines CNAME records for various original URLs. If aDNS query corresponding to a particular original URL matches an entry inthe data store, the DNS server component 118 returns a CNAME record asdefined in the data store. In an illustrative embodiment, the data storecan include multiple CNAME records corresponding to a particularoriginal URL. The multiple CNAME records would define a set of potentialcandidates that can be returned to the client computing device. In suchan embodiment, the DNS server component 118, either directly or via anetwork-based service, can implement additional logic in selecting anappropriate CNAME from a set of possible of CNAMEs. In an illustrativeembodiment, each DNS server component 118, 124, 130 maintains the samedata stores that define CNAME records, which can be managed centrally bythe CDN service provider 106. Alternatively, each DNS server component118, 124, 130 can have a POP specific data stores that define CNAMErecords, which can be managed centrally by the CDN service provider 106or locally at the POP 116, 122, 128.

The returned CNAME can also include request routing information that isdifferent from or in addition to the information provided in URL/CNAMEof the current DNS query. For example, if the CNAME selection is basedon regional plan, a specific regional plan can be identified in the“request_routing_information” portion of the specific CNAME record. Asimilar approach could be taken to identify service level plans and filemanagement by including a specific identifier in the“request_routing_information” portion of the CNAME record. In anotherembodiment, request routing information can be found in theidentification of a CDN service provider 106 domain different from thedomain found in the current URL/CNAME. For example, if the CNAME isbased on regional plan, a specific regional plan domain (e.g.,“cdnprovider-region1.com”) could be used in the domain name portion ofthe specific CNAME record. Any additional request routing informationcan be prepended to the existing request routing information in thecurrent URL/CNAME such that the previous request routing informationwould not be lost (e.g.,http://serviceplan.regionalplan.cdnprovider.com). One skilled in therelevant art will appreciate that additional or alternative techniquesand/or combination of techniques may be used to include the additionalrequest routing information in the CNAME record that is selected by theDNS server component 118.

With continued reference to FIG. 4, one skilled in the relevant art DNSserver component 118 may select (or otherwise obtain) a CNAME recordthat is intended resolve to a more appropriate DNS server of the CDNservice provider 106. It may be possible, however, that the same DNSserver would also be authoritative for the subsequent DNS query for theCNAME to be provided to the client computing device. For example, aspecific DNS server may be authoritative for both a specific regionalplan and a service level plan. Thus, returning a CNAME would stillresult in the DNS query arriving at the same DNS query (may due in partto the client computing device's geography). In such an embodiment, theDNS server, such as DNS server component 118, may choose to resolve thefuture DNS query in advance.

With reference now to FIG. 5, upon receipt of the CNAME from the DNSserver component 118, the client computing device 102 generates asubsequent DNS query corresponding to the CNAME. As previously discussedwith regard to FIG. 4, the DNS query process could first start with DNSqueries for the “.” and “com” portions, followed by a query for the“cdnprovider” portion of the CNAME. To the extent, however, that theresults of a previous DNS queries can be cached (and remain valid), theclient computing device 102 can utilize the cached information and doesnot need to repeat the entire process. However, at some point, dependingon whether the CNAME provided by DNS server component 118 (FIG. 4) andthe previous URL/CNAME share common CDN service provider domains,resolves to a different POP provided by the CDN service provider 106. Asillustrated in FIG. 5, the DNS server component 124 of POP 122 is nowauthoritative based on the different information in the current CNAMEpreviously provided by the DNS server component 118. As previouslydescribed, the DNS server component 124 can then determine whether toresolve the DNS query on the CNAME with an IP address of a cachecomponent that will process the content request or whether to provideanother alternative resource identifier selected in the manner describedabove.

For purposes of illustration, assume that the DNS server component 118determines that the DNS query corresponding to the current CNAME(provided by DNS server component 116) also corresponds to a CNAMErecord in its data store. In such an example, the DNS server component124 would do any necessary processing to select a specific CNAME andreturn the CNAME to the client computing device. With reference now toFIG. 6, the client computing device 102 would now transmit a secondsubsequent DNS query corresponding to the CNAME provided by DNS servercomponent 124 (FIG. 5). In accordance with DNS query processes alreadydescribed, the DNS query would illustratively be received by the DNSserver component 130 of POP 128. Again, the DNS server component 130 canthen determine whether to resolve the DNS query on the CNAME with an IPaddress of a cache component that will process the content request orwhether to provide another alternative resource identifier selected inthe manner described above. In this example, the DNS server component130 returns an IP address.

In an illustrative embodiment, the DNS server components, such as DNSserver component 130, can utilize a variety of information in selectinga resource cache component. In one example, the DNS server component candefault to a selection of a resource cache component of the same POP. Inanother example, the DNS server components can select a resource cachecomponent based on various load balancing or load sharing algorithms.Still further, the DNS server components can utilize network performancemetrics or measurements to assign specific resource cache components.The IP address selected by a DNS server component may correspond to aspecific caching server in the resource cache. Alternatively, the IPaddress can correspond to a hardware/software selection component (suchas a load balancer).

With reference now to FIG. 7, in an illustrative example, assume thatthe DNS server component 130 has selected the resource cache component132 of POP 128. Upon receipt of the IP address for the resource cachecomponent 132, the client computing device 102 transmits requests forthe requested content to the resource cache component 132. The resourcecache component 132 processes the request in a manner described aboveand the requested content is transmitted to the client computing device102.

With reference now to FIG. 8, a request routine 800 implemented by theCDN provider 106 will be described. One skilled in the relevant art willappreciate that actions/steps outlined for routine 800 may beimplemented by one or many computing devices/components that areassociated with the CDN service provider 106. Accordingly, routine 800has been logically associated as being performed by the CDN serviceprovider 106.

At block 802, one of the DNS server components 118, 124, 130 receives aDNS query corresponding to resource identifier. As previously discussed,the resource identifier can be a URL that has been embedded in contentrequested by the client computing device 102 and previously provided bythe content provider 104. Alternatively, the resource identifier canalso correspond to a CNAME provided by a content provider DNS server inresponse to a DNS query previously received from the client computingdevice 102. At decision block 804, a test is conducted to determinewhether the current DNS server is authoritative to resolve the DNSquery. In an illustrative embodiment, the DNS server can determinewhether it is authoritative to resolve the DNS query if there are noCNAME records corresponding to the received resource identifier.Alternative or additional methodologies may also be practiced todetermine whether the DNS server is authoritative.

If the current DNS server is authoritative (including a determinationthat the same DNS server will be authoritative for subsequent DNSqueries), the current DNS server resolves the DNS query by returning theIP address of cache server component. In a non-limiting manner, a numberof methodologies for selecting an appropriate resource cache componenthave been previously discussed. Additionally, as described above, the IPaddress may correspond to a specific cache server of a resource cachecomponent or generally to group of cache servers.

Alternatively, if at decision block 804 the DNS server is notauthoritative, at block 808, the DNS server component selects andtransmits an alternative resource identifier. As described above, theDNS server component can utilize a data store to identify an appropriateCNAME as a function of the current DNS query. Additionally, the DNSserver component can also implement additional logical processing toselect from a set of potential CNAMES. At block 810, different DNSserver components 118, 124, 130 receive a DNS query corresponding to theCNAME. The routine 800 then returns to decision block 804 and continuesto repeat as appropriate.

While illustrative embodiments have been disclosed and discussed, oneskilled in the relevant art will appreciate that additional oralternative embodiments may be implemented within the spirit and scopeof the present invention. Additionally, although many embodiments havebeen indicated as illustrative, one skilled in the relevant art willappreciate that the illustrative embodiments do not need to be combinedor implemented together. As such, some illustrative embodiments do notneed to be utilized or implemented in accordance with scope ofvariations to the present disclosure.

Conditional language, such as, among others, “can,” “could,” “might,” or“may,” unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or steps. Thus, such conditional language is notgenerally intended to imply that features, elements and/or steps are inany way required for one or more embodiments or that one or moreembodiments necessarily include logic for deciding, with or without userinput or prompting, whether these features, elements and/or steps areincluded or are to be performed in any particular embodiment.

Any process descriptions, elements, or blocks in the flow diagramsdescribed herein and/or depicted in the attached figures should beunderstood as potentially representing modules, segments, or portions ofcode which include one or more executable instructions for implementingspecific logical functions or steps in the process. Alternateimplementations are included within the scope of the embodimentsdescribed herein in which elements or functions may be deleted, executedout of order from that shown or discussed, including substantiallyconcurrently or in reverse order, depending on the functionalityinvolved, as would be understood by those skilled in the art. It willfurther be appreciated that the data and/or components described abovemay be stored on a computer-readable medium and loaded into memory ofthe computing device using a drive mechanism associated with a computerreadable storing the computer executable components such as a CD-ROM,DVD-ROM, or network interface further, the component and/or data can beincluded in a single device or distributed in any manner. Accordingly,general purpose computing devices may be configured to implement theprocesses, algorithms and methodology of the present disclosure with theprocessing and/or execution of the various data and/or componentsdescribed above.

It should be emphasized that many variations and modifications may bemade to the above-described embodiments, the elements of which are to beunderstood as being among other acceptable examples. All suchmodifications and variations are intended to be included herein withinthe scope of this disclosure and protected by the following claims.

What is claimed is:
 1. A method for request routing comprising:obtaining a domain name system (DNS) query from a client computingdevice at a first DNS server of a content delivery network (CDN) serviceprovider, wherein the DNS query corresponds to a requested resourceassociated with an original resource identifier provided by a contentprovider and wherein the CDN service provider is different from thecontent provider; obtaining an alternative resource identifier based oninformation associated with the client computing device and the contentprovider if the first DNS server is determined not to be authoritativeto the DNS query, wherein the alternative resource identifier includesinformation for causing a DNS query to resolve to a domain correspondingto the CDN service provider; causing transmission of the alternativeresource identifier to the client computing device; obtaining a secondDNS query from the client computing device at a second DNS server of theCDN service provider based on the alternative resource identifier; andif the second DNS server is determined to be authoritative to the secondDNS query, selecting a cache component for providing content associatedwith the original resource request and causing transmission of a networkaddress identifying the selected cache component to the client computingdevice, wherein the method is performed by one or more computing devicesof the CDN service provider.
 2. The method as recited in claim 1,wherein the information associated with the content provider includesfile information corresponding to the requested content and wherein thealternative resource identifier includes information identifying a fileprocessing plan provided by the CDN service provider.
 3. The method asrecited in claim 1, wherein the information associated with the clientcomputing device corresponds to a geographic location of the clientcomputing device.
 4. A system for request routing comprising: a firstdomain name system (DNS) server at a first point of presence of acontent delivery network (CDN) service provider, the first DNS servercomprising a hardware processor configured to executecomputer-executable instructions to: receive, from a client computingdevice, a first DNS query corresponding to a requested resourceassociated with an original resource identifier provided by a contentprovider, wherein the content provider is different from the CDN serviceprovider; if the first DNS server is determined not to be authoritativeto the first DNS query, obtain an alternative resource identifier basedon information associated with the client computing device and thecontent provider, wherein the alternative resource identifier includesinformation for causing a DNS query to resolve to a domain correspondingto the CDN service provider; and cause transmission of the alternativeresource identifier to the client computing device; and a second DNSserver at a second network point of presence of the CDN serviceprovider, the second DNS server comprising a hardware processorconfigured to execute computer-executable instructions to: receive, fromthe client computing device, a second DNS query based on the alternativeresource identifier; and if the second DNS server is determined to beauthoritative to the second DNS query, select a cache component forproviding content associated with the original resource request andcause transmission of a network address identifying the selected cachecomponent to the client computing device.
 5. The system as recited inclaim 4, wherein the information associated with the content providerincludes file information corresponding to the requested content andwherein the alternative resource identifier includes informationidentifying a file processing plan provided by the CDN service provider.6. The system as recited in claim 4, wherein the information associatedwith the client computing device corresponds to a geographic location ofthe client computing device.
 7. A method for request routing comprising:obtaining a domain name system (DNS) query from a client computingdevice at a first DNS server of a content delivery network (CDN) serviceprovider, wherein the DNS query corresponds to a requested resourceassociated with a first resource identifier; determining, at the firstDNS server responsive to the DNS query, that the first resourceidentifier is associated with an alternative resource identifier;causing transmission of the alternative resource identifier to theclient computing device, wherein the alternative resource identifierincludes information for causing a DNS query to resolve to a domaincorresponding to the CDN service provider; obtaining a subsequent DNSquery from the client computing device at a second DNS server of the CDNservice provider, wherein the subsequent DNS query is based on thealternative resource identifier provided by the CDN service provider;resolving the subsequent DNS query, at the second DNS server, toidentify a cache component for providing content associated with theoriginal resource request; and causing transmission of a network addressidentifying the identified cache component to the client computingdevice, wherein the method is performed by one or more computing devicesof the CDN service provider.
 8. The method as recited in claim 7,wherein first resource identifier corresponds to a uniform resourcelocator such that the DNS query resolves to a domain corresponding tothe CDN service provider.
 9. The method as recited in claim 7, whereinthe first resource identifier corresponds to an alternative resourceidentifier such that the DNS query resolves to a domain corresponding tothe CDN service provider.
 10. The method as recited in claim 7, whereinthe alternative resource identifier corresponds to a canonical namerecord identifier.
 11. The method as recited in claim 7, wherein thefirst resource identifier and the alternative resource identifierinclude information identifying a same domain corresponding to the CDNservice provider.
 12. The method as recited in claim 7, wherein thefirst resource identifier includes information identifying a firstdomain corresponding to the CDN service provider and wherein thealternative resource identifier includes information identifying asecond domain corresponding to the CDN service provider.
 13. The methodas recited in claim 7, wherein determining that the first resourceidentifier is associated with an alternative resource identifiercomprises: obtaining resource routing information corresponding to acontent provider associated with the requested content; selecting analternative resource identifier as a function of the resource routinginformation corresponding to the content provider associated with therequested content.
 14. The method as recited in claim 13, wherein theinformation associated with the content provider includes regionalservice information and wherein the alternative resource identifierincludes information identifying a regional service plan provided by theCDN service provider.
 15. The method as recited in claim 13, wherein theinformation associated with the content provider includes service levelinformation and wherein the alternative resource identifier includesinformation identifying a service level plan provided by the CDN serviceprovider.
 16. The method as recited in claim 13 further comprisingobtaining resource routing information corresponding to the clientcomputing device associated with the DNS query.
 17. A system for requestrouting comprising: a first network point of presence of a contentdelivery network (CDN) service provider and including a first domainname system (DNS) server that receives a DNS query from a clientcomputing device, wherein the DNS query corresponds to a requestedresource associated with a first resource identifier, and wherein thefirst DNS server comprises a hardware processor configured to executecomputer-executable instructions to: determine, responsive to the DNSquery, that the first resource identifier is associated with analternative resource identifier; and cause transmission of thealternative resource identifier to the client computing device, whereinthe alternative resource identifier includes information for causing aDNS query to resolve to a domain corresponding to the CDN serviceprovider; and a second network point of presence of the CDN serviceprovider and including a second DNS server that receives a subsequentDNS query from the client computing device, wherein the subsequent DNSquery is based on the alternative resource identifier, and wherein thesecond DNS server comprises a hardware processor configured to executecomputer-executable instructions to: resolve the subsequent DNS query toidentify a cache component for providing content associated with theoriginal resource request; and cause transmission of a network addressidentifying the identified cache component to the client computingdevice.
 18. The system as recited in claim 17, wherein the firstresource identifier corresponds to a uniform resource locator providedby the content provider such that the DNS query resolves to a domaincorresponding to the CDN service provider.
 19. The system as recited inclaim 17, wherein the alternative resource identifier corresponds to acanonical name record identifier.
 20. The system as recited in claim 17,wherein determining that the first resource identifier is associatedwith an alternative resource identifier comprises: obtaining resourcerouting information corresponding to a content provider associated withthe requested content; and selecting an alternative resource identifieras a function of the resource routing information corresponding to thecontent provider associated with the requested content.
 21. The systemas recited in claim 20, wherein the resource routing informationassociated with the content provider includes regional serviceinformation and wherein the alternative resource identifier includesinformation identifying a regional service plan provided by the CDNservice provider.
 22. The system as recited in claim 20, wherein theresource routing information associated with the content providerincludes service level information and wherein the alternative resourceidentifier includes information identifying a service level planprovided by the CDN service provider.
 23. The system as recited in claim20, wherein the resource routing information associated with the contentprovider includes file information corresponding to the requestedcontent and wherein the alternative resource identifier includesinformation identifying a file processing plan provided by the CDNservice provider.
 24. The system as recited in claim 17, wherein thefirst DNS server is further operative to obtain resource routinginformation corresponding to the client computing device associated withthe DNS query.
 25. The system as recited in claim 24, wherein theresource routing information corresponding to the client computingdevice associated with the DNS query comprises a geographic location ofthe client computing device.
 26. The system as recited in claim 24,wherein determining that the first resource identifier is associatedwith an alternative resource identifier is based on the resource routinginformation corresponding to the client computing device associated withthe DNS query.
 27. The system as recited in claim 17, wherein thenetwork address comprises a network address of a cache component in thesecond network point of presence.
 28. The system as recited in claim 17,wherein the network address comprises a network address of a cachecomponent in another network point of presence.